This is a renewal application from an established Program- Project which began with a cardiopulmonary theme but now focuses entirely on coronary circulatory control and pathophysiology. Current program structure includes four research areas and four supporting core units. Project I addresses mechanisms postulated to control coronary pressure- flow behavior, using experimental designs intended to deal with potentially confounding issues and thereby resolve currently controversial points. Project II continues ongoing studies of coronary input impedance, extending observations during diastole to the full cardiac cycle and also addressing systolic-diastolic flow interactions, effects of intramyocardial capacitance and the distribution of arterial components of capacitance. Project III addresses factors modulating autoregulatory responses to acute and chronic reductions in regional coronary artery pressure in conscious animals, emphasizing interactions among flow, function and pressure near the lower auto-regulatory limit of the traditional steady-state pressure-flow relationship. Project IV reflects the currently intense clinical and experimental interest in coronary reperfusion. Earlier studies of myocardial injury and recent animal and human studies during reperfusion indicate that myoglobin is a useful agent for detecting reperfusion noninvasively and evaluating several pertinent consequences. Overall Program-Project strategy continues to emphasizes scientific interaction among investigators whose personal research interests and efforts cross interdisciplinary lines, and whose activities are facilitated by collaborative endeavor in shared core laboratory facilities. The intend result is an innovative, stable program having a synergistic effect on both basic and applied coronary research.